Stabilized polymer blends

ABSTRACT

THE USE OF UP TO 20% BY WEIGHT OF ORGANIC ANHYDRIDES AS STABILIZERS IN POLYMER COMPOSITIONS CONTAINING AT LEAST 50 MOLE PERCENT OF POLYMERIZED UNSATURATED NITRILES SUCH AS ACRYLONTRILE AND METHACRYLONITRILE, AND AT LEAST 5% BY WEIGHT OF A DIENE RUBBER. THE ANHYDRIDES ARE SELECTED FROM ANHYDRIDES OF CYCLIC DICARBOXYLIC ACIDS, POLYMERIC ANHYDRIDES AND POLYMERIC ACIDS WHICH LOSE WATER ON HEATING TO FORM POLYMERIC ANHYDRIDES.

3,793,401 Ice Patented Feb. 19, 1974 3,793,401 STABILIZED POLYMER BLENDS Eric Nield and Philip Anthony Stanilantl, Welwyn Garden City, England, assignors to Imperial Chemical Industries Limited, London, England No Drawing. Filed Nov. 27, 1970, Ser. No. 93,390 Claims priority, application Great Britain, Nov. 27, 1969, 58,156/69 Int. C1. C08]? 45/58 US. Cl. 260-876 R 10 Claims ABSTRACT OF THE DISCLOSURE The use of up to 20% by weight of organic anhydrides as stabilizers in polymer compositions containing at least 50 mole percent of polymerized unsaturated nitriles such as acrylonitrile and methacrylonitrile, and at least by weight of a diene rubber. The anhydrides are selected from anhydrides of cyclic dicarboxylic acids, polymeric anhydrides and polymeric acids which lose water on heating to form polymeric anhyfdrides.

The invention relates to the stabilization of polymer compositions containing a diene rubber and polymerized units of an ethylenically unsaturated nitrile.

During melt processing of polymerizing nitriles such as acrylonitrile and methacrylonitrile where the polymer is subjected to high temperatures, considerable degradation can take place. This manifests itself as a darkening of the color, and as an increase in the melt viscosity of the polymeric material. The presence of a diene rubber increases the susceptibility to degradation, and in copolymers of acrylonitrile and methacrylonitrile this susceptibility also generally increases with increasing acrylontrile and methacrylonitrile content.

According to the present invention, we provide a composition oornprising (A) 80 to 99.9% by weight of a polymeric material having a resin component containing at least 50 mole percent of at least one polymerized ethylenically unsaturated nitrile and a rubber component containing a diene rubber where the diene rubber corn prises at least 5% by weight of the polymeric material, and (B) 0.1 to 20% by weight of a stabilizer selected from cyclic anhydride of cyclic dicarboxylic acids, polymeric anhydrides, and corresponding polymeric acids (and their derivatives) which lose water on heating to form the said polymeric anhydrides. The resin component of the polymeric material may be homopolymer of acrylonitrile or methacrylonitrile or a coploymer of acrylonitrile or methacrylonitrile with other ethylenically unsaturated compounds copolymerizable therewith, or a mixture of such polymers, where at least 50 mole percent of the resin component consists in units of the nitrile monomer or monomers. The diene rubber contains from 40 to 100% molar of at least one conjugated 1,3-diene monomer and from 0 to 60% molar of at least one other ethylenically unsaturated monomer copolymerizable with free radical catalysts. The diene rubber may be blended directly with the nitrile resin component, or it may form the substrate of graft copolymer on which is grafted a nitrile-containing superstrate. The stabilizers are particularly useful for the stabilization of blends of a resins which is a homopolymer or copolymer of an ethylenically unsaturated nitrile and a graft copolymer which comprises a diene rubber substrate and a nitrile-containing superstrate.

Degradation of nitrile-containing polymers which occurs at elevated temperatures, such as those employed during moulding, is thought to occur by a rearrangement of the nitrile groups to form a nitrogen bridge between adjacent nitrile carbon atoms, forming a second chain linked with the polymer carbon chain and composed of the repeated conjugated units Cross-linking is thought to be brought about by the formation of such a linkage between the nitrile carbon atoms on different polymerchains. As the proportion of comonomer units increases in a copolymer at the expense of acrylonitrile, the length of uninterrupted runs of consecutive acrylonitrile units is reduced, and hence the possibility of degradation diminishes. Thus, the stabilizers of the present invention are of particular interest where the resin component contains high quantities of nitrile, in particular when the resin component of the polymeric material comprises at least 70 mole percent of units of the polymerized nitrile.

The stabilizers of the present invention are particularly suitable for stabilizing graft copolymers comprising a substrate of a diene rubber and a superstrate of acrylonitrile and aromatic olefin in which the units of aromatic olefin are randomly distributed in the polymer molecule and in which the molar ratios of acrylonitrile to aromatic olefin in the range 2:1 to 9:1 as described in British specification 1,185,306 or within the range 9:1 to 20:1; polymeric material containing methacrylonitrile and a diene rubber as described in British specification 1,204,476; graft copolymers comprising a diene rubber substrate and a superstrate of an acrylonitrile copolymer where the comonomers are other than aromatic olefins as described in British specification 1,143,408; blends of the above grafts with compatible resins; random copolymers of acrylonitrile and aromatic olefins having molar ratios of acrylonitrile to aromatic olefins in the range 2:1 to 6:1 as described in British specification 1,185,305 or in the range 6:1 to 20:1 when they are blended with compatible diene rubber-based graft copolymers; copolymers of acrylonitrile and comonomers other than aromatic olefins as described and claimed in British specifications 1,086,673 and 1,088,758 when blended with compatible diene rubber-base graft copolymers.

The stabilizers are selected from cyclic anhydrides of cyclic dicarboxylic acids, polymeric anhydrides, and corresponding polymeric acids and their derivatives which lose water on heating to form the said polymeric anhydrides. Cyclic anhydrides of acyclic-unsaturated (1,}3-(llcarboxylic acids were also examined but none was found which provided any substantial stabilization. Among those which were found to be ineffective and which are outside the scope of the present invention are maleic and succinic anhydrides. Examples of the anhydrides of cyclic dicarboxylic acids which may be used according to the invention are phthalic anhydride, naphthalic anhydride and 3,6-endo-oxa-hexahydrophthalic (I) anhydride; of these the preferred anhydride is phthalic anhydride. The polymeric anhydrides may, for example, be maleic anhydride copolymers such as ethylene/maleic anhydride copolymer and u-methyl styrene/maleic anhydride copolymer. The polymeric acids may for example be methyl methacrylate/methacrylic acid copolymer, styrene/methacrylic acid copolymer or polyacrylic acid.

The quantity of stabilizer to be incorporated into the polymeric material depends on the degree of stabilization required and on the required mechanical properties. It will also depend on the proportion of anhydride or acid in the stabilizer selected. Thus, for example, when the selected stabilizer is a styrene/methacrylic acid copolymer, containing only a small proportion of methacrylic acid, a greater quantity of the copolymer would be required to achieve the same degree of stability than of a copolymer containing a larger amount of methacrylic acid. In general it is sufficient to use the stabilizers in quantities not greater than 20% by Weight of the polymeric material although for most purposes up to by weight of stabilizer is preferred. Although some improvement in the stability may generally be achieved by using as little as 0.1% by weight of the stabilizer, it is preferable to use at least 0.5 %by weight of the stabilizer.

The stabilizers may be incorporated into the polymeric material at any convenient time after the polymerization reactions forming the components of the polymeric material have been completed. Thus the polymeric stabilizers may be added to the polymerization reaction mixture before isolation of the polymeric material. When graft copolymers are latex blended with resins, it is very convenient to incorporate the stabilizers while carrying out the blending operation. However, for the monomeric stabilizers, that is the anhydrides of the cyclic, u, 3-dicarboxylic acids, susbtantial loss of stabilizer may occur during polymer work-up if they are incorporated in the sys tem before that stage. It is therefore preferable to incorporate the stabilizers, particularly the monomeric stabilizers, during compounding of the polymeric material. The polymeric matreials may also be mixed with any desired fillers and lubricants.

Compositions of the present invention may be fabricated by any method available to the processing of thermoplastic materials. The compositions can therefore be compression moulded; blow moulded; extruded; calendered and cast into films, moulded into plaques, bottles and other articles. The improved heat stability of the composition leads to generally satisfactory reprocessing.

In order to compare the stability of prepared materials at elevated temperatures, about g. of the material was loaded into a cylindrical container thermostatically controlled at the required temperature, generally about 260 C. The container had an internal diameter of 1 cm., and a length of cm. One end of the cylinder was fitted with a die having an internal diameter of 0.5 mm. and a length of 3.2 mm. The polymer was heated for three minutes, and then a small portion was extruded through the die by a ram moving at a speed of 0.0156 cm. s.- the polymer being extruded through the die at a shear rate of 1000 s.- The stress necessary to maintain this shear rate was measured using a pressure gauge fitted to the ram, and the viscosity calculated by the ratio of the measured stress to the shear rate. While maintaining the bulk of the material at a temperature of 260 C., further samples of the material were extruded at convenient time intervals. Observations of the changes with time of the viscosity, extrudate quality and color, were recorded as a measure of the thermal stability of the polymer melt at the measuring temperature.

The invention is illustrated by the following examples.

EXAMPLE 1 A rubber resin blend was prepared by blending a latex of a graft copolymer (comprising equal amounts of a substrate of polybutadiene and a superstrate of random acrylonitrile/styrene copolymer containing 75 mole percent acrylonitrile and mole percent styrene) and a resin latex (comprising a random acrylonitrile/styrene copolymer containing 75 mole percent acrylonitrile and 25 mole percent styrene), the ratio of the components being such that the final dry blend contained 10% polybutadiene. 2,6-di-tertiary-butyl-4-methylphenol (1% by weight of final blend) and diluaryl thiodipropionate (0.5% by weight of final blend) were added as aqueous dispersion to the latex blend prior to coagulation with an equal volume of a 1% aqueous magnesium sulphate solution at 75 C. The coagulum was washed with water, then twice 4 with methanol and finally twice with water, and then dried.

The anhydride stabilizers of the present invention were added to the dried blend powder and mixed in a Henschel mixer. The blend was then compounded on a Banbury mixer and finally on a two roll mill.

Blends containing 0, 1 and 2% of phthalic anhydride were prepared according to the above procedure and submitted to the ram extruder melt stability test at 260 C., as hereinbefore described. The blends were also injection moulded into discs 11.4 cm diameter and 0.32 cm. thick, and mechanical properties of these discs were measured. The results obtained are given in Table I.

After prolonged heating at 260 C., the viscosity of some of the materials showed a sudden increase, and the period of heating required to produce the sudden change in viscosity is given in the table as the time to set up. In each table, where the time to set up is given as greater than a specific time, the test was discontinued at that time. The Charpy notched impact test was carried out at room temperature (about 20 C.). A specimen 60 mm. long, 6.5 mm. wide and 3 mm. thick was given a 45 notch 2.5 mm. deep (tip radius 0.25 mm.) in the center of one edge. The specimen was supported between two supports 5 mm. apart and struck centrally on the edge opposite the notch by a pendulum dropping from 30 cm. with more than sufficient energy to break the specimen. From the residual energy of the pendulum, the energy required to break the specimen was calculated and divided by the cross sectional area of the specimen at the notch. The resulting value represents the energy required to break the material.

TABLE I Notched Percent phthalic impact Flexural anhydride (percent by Time to set up at strength, modulus, weight) 260 0. ft. lb/rn. dynes/cm.

0 50 minutes 6 2. 9X10 1 minutes 2 minutes 5. 7 8. 1x10 EXAMPLE 2 In the following experiments a blend as described in Example 1 was mixed with stabilizers identified in Table II. In compounds b and f, stabilizer was added to the powdered blend in a small powder mixer and then the sample compression moulded at about C., prior to testing on the ram extruder at 260 C. In compounds 0, d and e, the stabilizer was added to the blend in the manner described in Example 1.

TABLE II Time to set up at Stabilizer (percent by Weight) 260 C.

Compound 11.. None 65 minutes.

b-- 1% naphthalic anhydride. 90 minutes.

0. 1% phthalic anhydride Do.

(1 2% phthalic anhydride 110 minutes.

a .e 1% ethylene/maleic anhydride 70 minutes.

copolymer.

t 1% 3,6-endo-oxa-hexahydro- Do.

phthalie anhydride.

EXAMPLE 3 In this example blends of the graft copolymer and the resin were prepared as described in Example 1, except that in some cases methanol washing was omitted. Stabilizers were incorporated in the manner described for compounds b and f of Example 2. Results of the ram ex- TABLE VII truder test are given in Table III. Time to Stabilizer (percent Time to set become brown by weight) up at 260 C. at 260 0. Compound TABLE III w None 110 minutes"--- 90 minutes.

with/without x 5% polyacrylic acld. 140 minutes-.. 140 minutes. Stabilizer Timetosetup at methanol (percentby 260 0. Washing We claim. l weight) 1. A composition OOIDPllSlIlg (A) 80 to 99.9% by Commundweight of a polymeric material having a resin component 8 None minutes Without containing 50-100% molar of units of an ethylenically h 11011811 95 t D 10 ggh dfldi, es 0 unsaturated mtnle and 050% molar of an ethylemcally 1 275styrene/ 75 minutes unsaturated monomer copolymerizable therewith and a methacryllc k Nacid copolymer. rubber component containing 40-l00% molar of at least one 50 minute with, L 2% phthalic 80 Inmates one con ugated 1,3 d1ene monomer and from 060% anhydride, 15 molar of at least one other ethylemcally unsaturated mon- 111 2% Styrene/ Did Q Set omer copolymerizable therewith using a free radical catmethacrylic 90 minutes. acid copolymer. alyst where the d1ene rubber comprlses at least 5% by weight of the polymeric material, and (B) 0.1 to

by weight of a stabilizer selected from the group con- 20 sisting of phthalic anhydride, naphthalic anhydride and EXAMPLE 4 their hydrogenated derivatives, polymeric anhydrides con- In this example the graft copolymer consisted of a taining 50-100% molar maleic anhydride and 050% substrate of polybutadiene and a superstrate of acrylomolar of an alkene, polymeric anhydrides of 50-100% nitrile/isobutene (70/30 molar) copolymer in approximolar acrylic and/or methacrylic acid and 0-50% molar mately equal proportions by weight. of another monoethylenically unsaturated monomer co- The resin phase was a random acrylonitrile/styrene polymerizable therewith, and corresponding polymeric (80/20 molar) copolymer. The blend contained 10% rubacids which lose water on heating to form the said polyber and was coagulatcd with a 1% aqueous aluminium meric anhydride.

sulphate solution at 75 C., and washed with water. No 2. A composition according to claim 1 in which the methanol was employed in the washing. Stabilizer was nitrile is a member of the group consisting of acryloniaded as described in Example 1 and the results are retrile and methacrylonitrile.

cordedinTable IV. 3. A composition according to claim 1 in which the polymeric material is a blend of the resin component and a graft copolymer which comprises said rubber compo- TABLE IV nent as a substrate and said resin component as a super- Time to set Strate- Stabilizer (Percent by Weight) up at C 4. A composition according to claim 1 m which the sta- Compoundbilizer is present in concentration between 0.5% and 10% n Nona 25minutes. by weight. 0 2% phthalic anhydride 35 minutes.

40 5. A composition according to claim 1 in which the stabilizer is phthalic anhydride.

6. A composition according to claim 1 in which the sta- EXAMPLE 5 bilizer is a homopolymer and/or a copolymer of meth- Blends of graft copolymers and resins were prepared acrylic acid as described in Example 1, except for compounds w and accorqmg to damn I m which the stax which were coagulated with ethanol, and stabilizers blhzer T' F anhydnd? P- were added by the method described for compounds b A composltlon accordmg to clam m the form of and f of Exam 1e Th r sults obtain d n in a moulded article.

P e e e are give 9. A composition according to claim 8 in which the T bl V W a dVII.

a es n moulded article is a bottle.

10. A composition according to claim 1 in the form of TABLE v a film.

Time to References Cited gg g ggg y $333 93 gggggg g UNITED STATES PATENTS Compound- 2,841,569 7/1958 Rugg et a1 260 45.7 p None minutes--.--.-- 60111111111285. Lee gf gg ggg ig 3,352,820 11/1967 Bawn 260-45.75 666 616. (53:50 3,222,422 12/1965 Cohen 260 876 3,231,524 1/1966 Simpson 260 2.s 5.133? gmmutsw 60 3,442,980 5/1969 Grabowski Z60--880 gg g g ggg g ifl 3,489,821 1/1970 Witt et al. 260-876 men 3,549,725 12/1970 Rose et al. 260876 t.....-.:;:;:. fi7glsltlhfilglglfifilglio. 100 minutes.-. 100 minutes. 499 3/1970 Weitzel et a]. 260 876 me? p 3,314,914 4/1967 Suling et a1. 260-322 2,675,370 4/1954 Barrett 260 78.5 2,971,939 2/1961 Baer 260-785 TABLE VI 3,642,949 2/1972 Stafiord et a1. 260876 Time to 3,671,607 6/1972 Lee 260876 Stabilizer (percent Time to set become brown ,242,135 3/ 1966 Bown et al. 260-4535 by weight) up at 260 C. at 260 C. Compound- DONALD E. CZAJA, Primary Examiner ll-...'.. iiifliy r en'ejgati 390 113533651; gifiiifilts. WHITE Assistant Examiner $631353? US. 01. m1. 

